1. Field of the Invention
This invention relates to the manufacture of electronic circuit boards and, in particular, to a method and apparatus for wave soldering double sided pin-in-hole electronic components.
2. Description of Related Art
Wave solder is a common method of mass termination of electronic component or connectors to a circuit board by means of molten solder. A circuit board populated with pin-in-holes (PIH) electronic components or connectors is passed over a wave of molten solder. The molten solder wets the leads of the components and fills the plated-thru-holes (PTH) of the circuit board. The components after wave soldering are mechanically attached and electrically connected to the circuit board.
The methods of carrying and transporting the circuit board through the wave solder tool can either be accomplished with or without a solder pallet. The solder pallet can be used to minimize the circuit board distortion or selectively shield areas of the circuit board that do not require solder. The solder pallet may be transported on either a belt or finger conveyor system in the wave solder tool.
The conventional method of using a pallet in wave solder requires the circuit board to lay flush and parallel to the surface of the pallet. This requires the circuit board designer to use components that have minimum height on the bottom side of the circuit board. The typical thickness of a selective wave solder pallet is approximately 0.006 mm (150 mils). Usually pockets or recesses are milled into the pallet for bottom side component clearances.
Typical circuit board design will keep all wave solder PIH components on a common side of the circuit board. However, when a circuit board design deviates from the conventional design rule, such as by specifying double-sided PIH components, alternative methods of soldering in PIH components on both sides are needed. One such method is the use of a solder fountain that is normally used for a localized removal of a PIH component. The solder fountain process is generally not an efficient or robust method of volume manufacturing, since it is very labor intensive and optimal preheating and process control are not easily achieved. Another method is to use a compliant pin component that is press-fitted into the PTH. This method is dependent on the availability of the component in a compliant pin format.
Accordingly, it is desirable to have a wave solder method and pallet that can enable the soldering of PIH components on both side of circuit board using a wave solder tool.